What I noticed:
Car sounds a lot meaner, and loudest at 3/4000 rpm.
Seems to accelerate a bit faster than when standard. This air filter is just a standard open element K&N air filter. 

The bad things about this filter is that it sucks up hot air from the engine bay. This  has a lower concentration of oxygen in it which is what we need to bun more fuel and get more power. This air filter did not have the problem of size as the Pipercross one did (below), it could more than handle the volume of air the car was asking from it.

www.abdracing.com

This air filter was great in a lot of way. It had a cold ram-air effect which means air was constantly being pushed into it through its front tube feed (since it was connected to the front of the car). It also made a great 'rocket launching' noise, but what lets it down is firstly it's size. The one I had on the car was meant to be for the 4Motion but It always felt like the car was having a hard time breathing, it was too small. Secondly, it sucked up too much water in winter... I went through 3 MAFs just because of this filter.

Although the TTDA is very similar in the way it works, no problems so far as far as rain is concerned. Just like this air filter, the TTDA also has a slight ram-air effect

www.pipercross.net